Advanced Electronic Signature (AES), Simple (SES) and Qualified (QES): The 3 eIDAS Levels

The electronic signature advanced (AES) is the most widely used level in B2B and the only one that offers a legal presumption of integrity without requiring a smart card for the signatory. Alongside the simple signature (SES) and the qualified signature (QES), it makes up the three levels defined by the European eIDAS regulation. Here is how to choose the right level depending on the nature of your document, its expected evidentiary value and the level of friction acceptable for the signatory.

What is the advanced electronic signature (AES)?

The advanced electronic signature is the intermediate level defined by Article 26 of the eIDAS regulation. It must fulfil four cumulative conditions: (1) be uniquely linked to the signatory, (2) be capable of identifying them, (3) be created using data that the signatory can, with a high level of confidence, use under their sole control, (4) be capable of detecting any subsequent alteration of the signed document. In practice, these conditions are met through strong authentication (email + SMS OTP), a time-stamped audit trail and a cryptographic hash of the PDF.

AES benefits from a legal presumption of integrity and origin that reverses the burden of proof before a judge: it is up to the party disputing the signature to prove it is false, not up to the signatory to prove its validity. This is what fundamentally distinguishes AES from SES, where reliability is assessed on a case-by-case basis by the judge.

The three levels defined by eIDAS

The European eIDAS regulation (No. 910/2014) organises electronic signature into three levels, corresponding to increasing degrees of requirement in terms of signatory identification and strength of evidence. Understanding these levels well makes it possible to choose the signature suited to each document, without over-engineering the process.

Level 1: the simple electronic signature (SES)

The simple electronic signature is the basic level. It corresponds to any electronic expression of consent: a click on "I accept", a checkbox, an initial drawn on a touchscreen.

• Requirements: clear consent, minimal identification (email)
• Evidence: weak to moderate, varies by provider
• Use case: quotes, purchase orders, internal agreements, terms and conditions
• Signatory friction: almost none — the signatory does not create an account

SES is sufficient for the vast majority of everyday commercial exchanges where the risk of dispute is low. It remains legally valid, with the judge assessing the reliability of the process on a case-by-case basis.

Level 2: the advanced electronic signature (AES)

The advanced signature strengthens the identification of the signatory and establishes a unique link between them and the document. It rests on four criteria set out in Article 26 of eIDAS:

1. it is uniquely linked to the signatory
2. it enables the signatory to be identified
3. it is created using means that the signatory can keep under their sole control
4. it is linked to the document in such a way that any subsequent alteration can be detected

In practice, AES relies on two-factor authentication: a unique link sent by email + an OTP code received by SMS. The final PDF includes a timestamp and a detailed audit trail.

• Use case: employment contract, lease, mandate, high-stakes commercial contract, NDA
• Signatory friction: low — an SMS code to enter in addition to email
• Evidence: strong, rebuttable presumption of validity

Level 3: the qualified electronic signature (QES)

The qualified signature is the highest level. It relies on a qualified certificate issued by a qualified trust service provider (QTSP) listed on the trusted list of an EU Member State, and on a secure signature creation device (e.g. YubiKey, smart card).

• Legal value: equivalent to a handwritten signature throughout the EU
• Use case: authentic instruments, public procurement contracts, certain notarial deeds
• Signatory friction: high — face-to-face or video KYC identity verification
• Cost: significantly higher than SES/AES

For most companies, QES is rarely necessary on a day-to-day basis. It becomes essential when the law requires it (legal proceedings, certain public procurement contracts) or when the contract has exceptional value.

Quick comparison table

How to choose the right level

The simple rule: align the level with the stakes of the document.

• If the document is disputed, what is at stake? A few hundred euros or a contract worth several tens of thousands?
• Is the relationship with the signatory known (long-standing customer) or unknown (first contact)?
• Does the document fall under a legal framework requiring a specific level (e.g. employment contract, lease) ?

As a general rule: SES for simple agreements, AES for anything related to HR, real estate, finance, QES only when the law requires it.

Common mistakes

• Systematically opting for QES "to be on the safe side": unnecessary friction for the signatory, high cost, often over-engineered.
• Relying on SES for everything: in the event of a dispute over an employment contract, the absence of strong authentication can weaken the evidence.
• Confusing validation with signature: an acknowledgement of receipt is not a signature.

How Certyneo helps you

Certyneo natively supports the simple (SES) and advanced (AES) levels, with dual email + SMS OTP via Twilio Verify for AES. For cases requiring QES, Certyneo interfaces with several European qualified providers (Docaposte Certigna, Universign, CertEurope) to trigger the qualified signature without changing tools.

You can set the signature level document by document depending on the stakes — or by template if you have industrialised a process.

Discover the Certyneo electronic signature solution

FAQ

Can I mix levels within the same envelope?

Yes. A multi-document envelope can include, for instance, a quote signed with SES and a contract signed with AES. Each signatory sees the authentication suited to the document they need to sign.

Is the advanced signature recognised internationally?

Within the EU, yes, under the principle of mutual recognition of eIDAS. Outside the EU, recognition depends on the local legal framework — this should be checked according to the jurisdiction concerned.

Is a personal certificate required to sign with AES?

No. AES can be obtained without a prior personal certificate thanks to dual OTP. This is what makes AES very accessible, whereas QES requires a qualified certificate.

Is a qualified signature mandatory for an employment contract?

No. The employment contract accepts the advanced signature (AES), which already offers a strong presumption of validity. For more details, see electronic signature of the employment contract.

How do I check the level of a signed document?

Open the PDF in Adobe Acrobat Reader: the signature properties display the level, the signatory and the timestamp. You can also use an online verifier.

Conclusion

Choosing the right level of electronic signature means finding the right balance between evidentiary value and friction for the signatory. Start simple, step it up a level when the legal stakes require it.

Try Certyneo to send, sign and track your documents online simply, quickly and securely.